The present invention relates in general to a Caller Identification (Caller ID) receiving device, and more particularly to a novel device for decoding a Frequency-Shift Keying (FSK) signal which carries Caller ID information and other telephone network service operations.
Caller ID services provided by telephone companies have been found to be highly useful. By employing a Caller ID device which decodes Caller ID information sent via the telephone line, a user is able to view a caller's identity in a display area of the Caller ID device. Three types of Caller ID services and devices are presently in use. A first, and most basic, type is "on-hook" Caller ID, which displays Caller ID information when the telephone is not in use, i.e., when the telephone is in an on-hook state. A second type is "off-hook" Caller ID, which, in addition to on-hook Caller ID services, displays incoming Caller ID when the telephone is in use, i.e., when the telephone is in an off-hook state. Still yet a third type is called "Caller ID Deluxe," which, in addition to off-hook Caller ID, provides a set of function keys to access various network services. Caller ID Deluxe displays Caller ID information as well as information about accessible network services. A Caller ID Deluxe user decides which network service to use and accesses it by using a set of function keys.
Each of the three types of Caller ID devices first decode an incoming FSK signal, which contains encoded Caller ID information. Caller ID devices available in the market as either stand-alone add-on models or devices integrated with a telephone use complicated hardware FSK decoder circuitry for receiving Caller ID information. Such hardware decoder circuits are both costly and prone to reliability problems. Another option for FSK decoding that is presently available uses Digital Signal Processor technology. However, such technology is prohibitively expensive for standard Caller ID devices. The present invention is a new method and apparatus for inexpensive and reliable FSK decoding. Telephones and associated adjunct assets, such as a Caller ID unit, are mass market consumer products requiring minimal cost in order to effectively compete in the marketplace.
For off-hook Caller ID and Caller ID Deluxe, incoming Caller ID information arrives at any time while the telephone is in use, i.e. off-hook. The existing industry practice is to receive off-hook Caller ID when only one Caller ID device is in use. No off-hook Caller ID is received if multiple Caller ID devices are connected to the same line and in use simultaneously. The reason is that before transmission of off-hook Caller ID, a Caller ID device replies to an incoming telephone signal with a dual-tone multifrequency (DTMF) tone as an acknowledgment, in what is known as the handshaking sequence. If multiple Caller ID devices are in use simultaneously, or if, due to inevitable minor variations in the manufacturing of the devices, out of synchronization, the acknowledgment tone is distorted and the handshaking sequence fails.
More recently, a telephone device from Northern Telecom has been disclosed as capable of allowing multiple telephone devices connected to the same line to receive off-hook Caller ID simultaneously. This device first detects which unit among multiple units connected to the same line is the first to go to an off-hook status. The unit that goes off-hook first is designated as the master phone. Only the master phone will send the acknowledgment tone during the handshaking sequence for receiving off-hook Caller ID, thus ensuring that the acknowledgment tone is not distorted. However, this device has several disadvantages. First, detection of which unit goes off-hook first may fail due to noisy or otherwise unfavorable telephone network conditions, resulting in the wrong unit being designated as the master phone. Second, if two units go off-hook substantially simultaneously, the system may be unable to detect which unit goes off-hook first, resulting in a situation where no phone is designated master. It is therefore an objective of the present invention to provide a reliable and cost-effective method and apparatus for allowing multiple Caller ID devices to receive off-hook Caller ID simultaneously.
Caller ID Deluxe devices sometimes include a set of function keys. Each function key corresponds to, and is labeled with, an available network service operation. Examples of network services accessible with the function keys are: conference call; block call; etc. Alternatively, a network service may be one using an Interactive Voice Response (IVR) system. In an IVR system, after a user establishes a connection to an IVR server, the IVR audibly plays a menu of available operations to the user using a prerecorded voice message. After listening to a voice menu, the user may press one or several digit keys on a telephone to indicate his/her choice. A DTMF tone or a sequence of DTMF tones corresponding to the keys pressed are sent to the IVR server. The server then performs the appropriate operation according to the user's choice.
One of the most popular IVR services provided by telephone companies is voice mail. Voice messages intended for a user are recorded in a voice mail server. A user may later listen to the messages intended for him/her by using an IVR voice mail system. Typical voice mail operations that may be selected by DTMF tones include: playing a message; rewind; fast forward; skipping a message; saving a message; and, erasing a message.
Network services are more conveniently accessed by providing standard Caller ID devices with a set of function keys appropriate to the system. Operation of the keys automatically leads to generating a DTMF tone sequence used for accessing a service, so that the user does not have to memorize a sequence of codes required for each service. A disadvantage of such a device is that different network service providers use different DTMF tones for accessing a network services operation. A device with specific function keys programmed to access network services provided by one telephone company often cannot work with network services provided by another. The problem is more profound in the case of IVR services, as differences in the command codes used by different IVR services providers are likely to be greater. As a result, the utility of such a device is limited. Such a device may allow the user to manually change the DTMF tones generated by each function key, but doing so for the entire set of function keys would be both time consuming and inefficient.